Crystallization processing for semiconductor applications

ABSTRACT

A method and apparatus for forming a crystalline semiconductor layer on a substrate are provided. A semiconductor layer is formed by vapor deposition. A pulsed laser melt/recrystallization process is performed to convert the semiconductor layer to a crystalline layer. Laser, or other electromagnetic radiation, pulses are formed into a pulse train and uniformly distributed over a treatment zone, and successive neighboring treatment zones are exposed to the pulse train to progressively convert the deposited material to crystalline material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/175,110, filed Feb. 7, 2014, which is a continuation of U.S. patentapplication Ser. No. 13/679,633, filed Nov. 16, 2012, which is acontinuation of U.S. patent application Ser. No. 12/953,103, filed Nov.23, 2010, which claims the benefit of U.S. provisional patentapplication Ser. No. 61/265,312, filed Nov. 30, 2009, all of which areincorporated herein by reference.

FIELD

Embodiments described herein relate to manufacture of semiconductordevices. More specifically, embodiments described herein relate toforming crystalline semiconductor layers for energy, memory, logic, orphotonic devices.

BACKGROUND

Photovoltaic energy generation was the fastest growing energy source in2007. In 2008, installed photovoltaic capacity increased approximately ⅔to about 15 GW. By some estimates, the global market for photovoltaicpower will grow at a compound annual rate of 32% between 2008 and 2013,reaching over 22 GW, while installed capacity grows at an average rateof 20-30% per year or more, possibly reaching 35 GW by 2013. Withavailable solar resources estimated at 120,000 TW, using less than0.013% of these available resources could replace fossil fuels andnuclear energy as sources of electrical power. Total global energyconsumption of 16 TW in 2005 is less than 0.02% of available solarenergy incident on the earth.

With so much potential, countries and companies around the world areracing to increase efficiency, and lower cost of, photovoltaic powergeneration. In a typical solar cell, a semiconductor material is exposedto sunlight to mobilize electrons. Some portions of the semiconductormaterial are doped with electron-rich elements, and other portions aredoped with electron-deficient elements to provide a driving force forthe mobilized electrons to flow toward current collectors. The electronsflow from the current collectors out to an external circuit to provideelectrical power.

The crystal structure of the semiconductor material influences the lightabsorption characteristics of the cell and the efficiency with which itconverts light into electricity. In an amorphous semiconductor material,there are few straight paths for electrons to travel, so electronmobility is less, and the energy required to render the electrons mobileis higher. Amorphous silicon materials thus have a larger band gap andabsorb light that has a shorter wavelength than light absorbed by acrystalline silicon material. Microcrystalline materials ornanocrystalline materials have some crystal structure, which gives riseto higher electron mobility on average, and lower band gap.Polycrystalline and monocrystalline materials have even higher mobilityand lower band gap.

While it is desirable to include absorbers having different morphologiesto capture more of the incident spectrum, only small amounts of, forexample, amorphous materials are needed to provide the absorbancebenefit. Too much amorphous material results in lower efficiency becauseelectrons travel comparatively slowly through the amorphous material,losing energy as they go. As they lose energy, they become vulnerable toShockley-Read-Hall recombination, falling out of the conduction bandback into the valence of an atom, recombining with a “hole”, or localelectron deficiency, and losing the absorbed solar energy that mobilizedthem.

To reduce this effect, it is thus desirable to maximize thepolycrystalline and monocrystalline morphologies in a solar cell. Thisis generally problematic, however, because production of polycrystallineand monocrystalline materials is slow, due to the need to grow crystals.The comparatively slow production rates require large investment for agiven productive capacity, driving up the cost of producing efficientsolar cells and panels.

Production of polycrystalline and monocrystalline materials is alsouseful for certain memory applications, such as 3D memory, and forvertical monolithic integration of various semiconductor devices, suchas photonic devices.

Thus there is a need for a method of manufacturing polycrystalline andmonocrystalline semiconductor phases efficiently and at high rates.

SUMMARY

Embodiments described herein provide a method of reorganizing thestructure of a solid material by exposing the solid material to pulsesof energy to progressively melt the solid material, forming a moltenmaterial, and recrystallizing the molten material.

Other embodiments provide a method of forming a solar cell, comprisingforming large crystal domains in an active layer of the solar cell byprogressively melting and recrystallizing the active layer using pulsesof spatially uniform laser light.

Other embodiments provide a method of forming a memory device,comprising forming a first conductive layer on a substrate, forming apolycrystalline or monocrystalline semiconductor layer on the substrateby a process comprising depositing a semiconductor layer on thesubstrate, progressively melting the semiconductor layer by exposing thesemiconductor layer to pulses of energy, forming a molten semicondutorlayer, and recrystallizing the molten semiconductor layer, and forming asecond conductive layer on the substrate.

Other embodiments provide a method of forming a photonic device,comprising forming a compound semiconductor layer over a ceramicsubstrate, and crystallizing the compound semiconductor layer bydirecting pulses of energy toward the compound semiconductor layer,progressively melting the compound semiconductor layer to form a moltenlayer, and crystallizing the molten layer to form a crystalline compoundsemiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A is a flow diagram summarizing a method according to oneembodiment.

FIG. 1B schematically illustrates pulses of energy according to anembodiment described herein.

FIG. 2 is a schematic cross-sectional view of an apparatus according toanother embodiment.

FIG. 3A is a flow diagram summarizing a method according to anotherembodiment.

FIG. 3B is a schematic cross-sectional view of a thin film solar cellaccording to another embodiment.

FIG. 4A is a plan view of a processing system according to anotherembodiment.

FIG. 4B is a schematic cross-sectional view of a processing chamberaccording to another embodiment.

FIG. 5A is a flow diagram summarizing a method according to anotherembodiment.

FIG. 5B is a schematic cross-sectional view of a crystalline solar cellaccording to another embodiment.

FIG. 6 schematically illustrates pulses of energy according to anembodiment described herein.

FIG. 7 is a schematic cross-sectional view of a device according toanother embodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Embodiments described herein generally provide methods and apparatus forforming solar cells, memory devices, and photonic devices such aslight-emitting diodes (LEDs). FIG. 1A is a flow diagram summarizing amethod 100 according to one embodiment. The method 100 is generallyuseful for rapidly forming crystalline semiconductor layers on asubstrate. The method 100 may be used in crystalline or thin-film solarcell manufacturing processes to make high-efficiency solar cells, memorydevices, logic devices, and photonic devices having crystallinesemiconductor phases. At 102, a semiconductor layer is formed on asubstrate. The substrate may be used in a thin film solar cell device,wherein the substrate is a glass substrate having a transparentconductive coating that forms an electrical contact layer that isdisposed on one surface of the substrate. In general, for thin filmsolar cells, a transparent, or nearly transparent, substrate yields thehighest sunlight absorption and thus improves the solar cell's poweroutput. The semiconductor material used to form one of the abovementioned devices may comprise an element, such as silicon, germanium,or other elemental semiconductor, or a compound semiconductor, such assilicon-germanium, a CIGS material, or a group III/V semiconductor. Thesemiconductor material may, additionally, be doped with a p-type dopant,such as boron, or with an n-type dopant, such as phosphorus, to form anelectron-rich or electron-deficient layer. The semiconductor materialmay have a crystal morphology that includes amorphous, polycrystalline,microcrystalline, and large-grain microcrystalline. In some embodiments,the semiconductor material may form an active layer of a solar cell orpanel.

The semiconductor material may be formed on the substrate using anyconvenient process. In most embodiments, a vapor deposition process,such as physical or chemical vapor deposition, with or without plasmaassistance, is used. In one particular embodiment, plasma-assistedchemical vapor deposition is used to deposit an amorphous silicon layerfrom a gas mixture comprising a silicon source, such as silane, hydrogengas, and optionally an inert gas, such as argon or helium. A dopantsource, such as borane, diborane, phosphine, or arsine, may be added tothe gas mixture to deposit a doped silicon layer. In one exemplaryembodiment used to form an intrinsic silicon layer in a solar celldevice, silane is provided to a processing chamber at a flow rate ofbetween about 1 sccm/L and about 10 sccm/L (normalized to the processingvolume of the chamber, in liters), with the ratio of hydrogen to silaneabout 20:1 or less by volume. RF power may be applied to the gasmixture, for example by coupling an RF source to the gas distributor, ata power level between about 15 mW/cm² and about 200 mW/cm² (normalizedto surface area of the substrate being processed, in square-centimeters)at a pressure between about 1 Torr and about 4 Torr. The semiconductormaterial may be formed to a thickness up to about 1 μm.

At 104, the semiconductor layer is exposed to pulses of electromagneticradiation. A plurality of treatment zones is generally defined on thesubstrate and exposed to the pulses sequentially. In one embodiment, thepulses may be pulses of laser light, each pulse having a wavelengthbetween about 200 nm and about 1200 nm, for example about 1064 nm asdelivered by a frequency-doubled Nd:YAG laser. Other wavelengths, suchas infrared, ultraviolet, and other visible wavelengths, may also beused. Other types of radiation, such as microwave radiation, may also beused. The pulses may be delivered by one or more sources ofelectromagnetic radiation, and may be delivered through an optical orelectromagnetic assembly to shape or otherwise modify selectedcharacteristics of the pulses.

At 106, the semiconductor layer is progressively melted by treatmentwith the pulses of electromagnetic radiation. Each pulse ofelectromagnetic radiation, for example laser light, may have energyenough to melt the portion of the substrate on which it impinges. Forexample, each pulse may deliver energy between about 0.3 J/cm² and about1.0 J/cm². A single pulse impacts the substrate surface, transferringmuch of its energy into the substrate material as heat. The first pulseimpacting the surface impacts a solid material, heating it to atemperature at or above its melting point, melting the impacted surfaceregion. Depending on the energy delivered by the first pulse, thesurface region may melt to a depth of between about 60 Å and about 600Å, leaving a layer of molten material on the surface. The next pulse toreach the surface impacts the molten material, delivering heat energythat propagates through the molten material into the underlying solidmaterial, melting more of the solid material. In this way, successivepulses of electromagnetic radiation may form a melt front that movesthrough the semiconductor layer with each successive pulse.

FIG. 1B is a schematic view of an example of an array of uniformelectromagnetic energy pulses 120 ₁-120 _(N) that are delivered to thesubstrate surface by one or more electromagnetic radiation device, suchas one or more of the emitters 224 discussed below. It should be notedthat the amount of energy delivered within each pulse (e.g., pulse 120₁, 120 ₂ . . . 120 _(N)) can be varied as a function of time, and thusthe profile of each pulse (e.g., energy versus time) can be varied asnecessary to improve the delivery of energy to the molten material. Forexample, the shape of pulse 120 ₁ need not be Gaussian shaped, as shownin FIG. 1B, and can be configured to deliver more energy at start of thepulse or at the end of the pulse (e.g., triangular shaped).

Each pulse may have the same amount of energy as the pulse before it, orone or more pulses may contain a different amount of energy. Forexample, the first pulse may have a lower amount of energy thansubsequent pulses, as shown in FIG. 1B, because the first pulse does notneed to propagate through a layer of molten material to reach a solidphase. In some embodiments, the plurality of pulses delivered to aregion of the semiconductor layer may comprise a first portion and asecond portion, wherein each pulse of the first portion has a differentenergy and each pulse of the second portion has the same energy. Asdescribed above, the first portion may comprise only one pulse withenergy different from the pulses of the second portion. In anotherembodiment, the first portion may have multiple pulses, each with moreenergy than the prior pulse, so that each pulse of the first portiondelivers more energy than the last.

In one embodiment, each pulse has a duration between about 1 nsec andabout 50 nsec, such as between about 20 nsec and about 30 nsec. Inanother embodiment, each pulse delivers power between about 10⁷ W/cm²and about 10⁹ W/cm². The pulses may be separated by a rest duration,which may be selected to allow a portion of the energy delivered by eachpulse to dissipate within the semiconductor layer. In one embodiment,the rest duration is chosen such that a pulse impacts the surface of thesemiconductor layer before enough heat is conducted away from the moltenmaterial to re-freeze 25% of the molten material. In another embodiment,each pulse generates a temperature wave, part of which propagatesthrough the phase boundary between liquid and solid, and part of whichis reflected back through the liquid phase, and the rest duration ischosen such that a second pulse impacts the surface before the reflectedtemperature wave from an immediately prior first pulse reaches thesurface. In one embodiment, the pulses overlap in time, so that theradiant intensity from a second pulse arrives at the surface before theradiant intensity from an immediately prior first pulse decays to zero.An overlap factor may be defined as the percent peak intensity of thefirst pulse impacting the surface at the time radiant intensity from thesecond pulse begins impacting the surface. In one embodiment, the pulsesmay have overlap factor between about 0% and about 50%, such as betweenabout 10% and about 40%, for example about 25%.

The pulses illustrated in FIG. 1B overlap in time, as may be practicedin many embodiments. The first pulse 120 ₁ has a peak intensity I_(P1)of energy delivered to the surface of the substrate. As the energyintensity at the substrate surface declines from the peak intensityI_(P1), energy from the second pulse 120 ₂ begins impacting thesubstrate surface at time t_(O), before the energy from the first pulsehas subsided. At time t_(O), the energy intensity from the first pulseis I_(O). Thus, the overlap factor for the first two pulses is100×(I_(O)/I_(P1)), as defined above. The cumulative energy incident onthe substrate surface from the added effect of the first and secondpulses 120 ₁ and 120 ₂ thus reaches a non-zero minimum I_(min) as shownby the cumulative energy curve 121.

In some embodiments wherein pulses overlap in time, each pulse mayextend the melt front between about 60 Å and about 600 Å, while the meltfront may recede between about 30 Å and about 100 Å during the restduration as heat conducts from the liquid phase into the solid phase.The number of pulses, the intensity and duration of each pulse, and theoverlap factor of the pulses inter-depend on the thickness of thematerial to be melted, ambient pressure of the processing environment,crystal structure of the material to be melted and composition ofmaterial to be melted.

The non-uniformity of a pulse may be defined as the average percentdeviation of radiant intensity at each point in the treatment zone fromthe average intensity over the entire treatment zone. A laser spotunaltered by any optics naturally has a Gaussian intensity distributionat any point in time. It should be noted that the Gaussian intensitydistribution of a laser spot on a surface is not to be confused with theGaussian energy-time profile of a pulse, as described above. The twoprofiles are independent, the intensity distribution being determined ata single point in time, or averaged over a duration, and the energy-timeprofile representing energy over time delivered to a point on thesurface, or averaged over the surface. For an unaltered laser spot, if atreatment zone is defined as all points receiving at least 5% of peakintensity from a Gaussian spot at any given point in time, then theaverage intensity across the treatment zone at any point in time will beabout 45% of peak intensity, and the non-uniformity of the Gaussian spotwill be about 80%.

In one embodiment, each pulse of electromagnetic radiation is spatiallyuniform or uniformly distributed over a treatment zone of the substrate.Each pulse may have non-uniformity less than about 5%, for example lessthan about 3%, or between about 1% and about 2.5%. In one embodiment,each treatment zone may have a rectangular shape, and in someembodiments, each treatment zone may have a square shape. In oneparticular embodiment, each treatment zone is a square approximately 2cm on each side, and each laser pulse is distributed over the 4 cm²treatment zone with non-uniformity less than about 2.5%. In such anembodiment, the surface of the treatment zone is melted to a veryuniform depth with each pulse.

In one embodiment, a train of overlapping pulses of electromagneticenergy form a continuous amplitude modulated beam of electromagneticenergy, wherein the frequency of the amplitude modulation is related tothe number and duration of pulses and the characteristics of the opticalcolumn used to form the pulses into an energy train. The pulse additiveamplitude modulated energy beam may be further homogenized to achievethe desired spatial uniformity as described above.

At 108, the melted portion of the semiconductor layer is recrystallizedto form a crystalline layer, such as a polycrystalline, multicrystallineor monocrystalline layer. The melted portion begins freezing at thesolid-liquid interface with other portions of the semiconductor layer.Because crystalline materials conduct heat better than amorphousmaterials, and crystalline materials with large grains conduct heatbetter than crystalline materials with small grains, for reasons similarto those described above with respect to electron mobility,incrementally more heat is conducted away by adjacent crystallinedomains, resulting in earlier freezing near phase boundaries withcrystalline domains. As freezing occurs, atoms align with the crystalstructure of the solid domain, propagating the adjacent crystalstructure through the liquid phase as it freezes. In this way, eachrecrystallized polycrystalline or monocrystalline treatment zone seedsrecrystallization of the next treatment zone.

In one embodiment, recrystallization of the melted portion may befacilitated directionally by delivering pulses of energy during therecrystallization operation. Because surface regions may lose heatfaster than internal regions of the molten layer due to radiation and/orconduction of heat into the ambient environment, pulses of energy may bedelivered to the substrate as recrystallization progresses to keepsurface regions from freezing before internal regions. Pulses deliveredduring recrystallization will have different profiles from pulsesdelivered during melting, to avoid re-melting the layer. For example, Npulses each having duration D_(N) may be delivered to melt the layer,and M pulses each having duration D_(M) may be delivered duringrecrystallization, where D_(N)>D_(M). Likewise, the instantaneousintensity or amount of energy delivered in each pulse may be lower,and/or the frequency of pulses may be lower. By controlling the meltingand recrystallization process the grain size of the recrystallized layercan be controlled. In one embodiment, the treatment process is used torecrystallize a silicon layer so that the grain size of the processedlayer is greater than about 1 micrometer (μm), and more preferablegreater than about 1000 μm. It is believed that larger grain sizes inthe recrystallized layer will improve the carrier lifetime andefficiency of a formed solar cell device by reducing the grain boundarysurface area that act as carrier recombination sites.

In one embodiment, a crystalline seed may be established on thesubstrate prior to forming the semiconductor layer on the substrate.Melt annealing may begin with a treatment zone in contact with thecrystalline seed to start the crystal growth process. Treatment may thenproceed by adjusting the electromagnetic energy delivery position toform adjacent treatment zones across the substrate to recrystallize theentire layer. In this way, a semiconductor phase may be converted to acrystalline morphology more rapidly than by depositing a crystallinephase from a vapor phase. In one example, it has been found that thedeposition rate in a 2.2 m×2.6 m a PECVD deposition chamber for anamorphous silicon layer is about 650 angstroms/min (Å/minute) and thedeposition rate of a microcrystalline silicon film in the same chamberis about 360 Å/minute. Therefore, it can take an additional 52 minutesto form a 1.5 micron (μm) microcrystalline silicon layer used in abottom cell of a tandem junction solar cell versus an amorphous siliconlayer using a vapor phase deposition process. Therefore, as long as themelt annealing device (e.g., reference numeral 455 in FIG. 4A) can treatthe complete substrate surface, at a rate equal or greater than thethroughput of solar cells through the production system 490 (FIG. 4A),the production line throughput can increased using the processesdescribed herein.

FIG. 2 is a schematic cross-sectional view of an apparatus 200 accordingto another embodiment. The apparatus 200 may be used to form devices andlayers as described elsewhere herein. The apparatus generally comprisesa chamber 201 with a substrate support 202 disposed therein. A source ofelectromagnetic energy 204 is disposed in the chamber, or in anotherembodiment may be disposed outside the chamber and may deliver theelectromagnetic energy to the chamber through a window in the chamberwall. The source of electromagnetic energy 204 directs one or more beamsof electromagnetic energy 218, such as laser beams or microwaveradiation, from one or more emitters 224 toward an optical assembly 206.The optical assembly 206, which may be an electromagnetic assembly,forms the one or more beams of electromagnetic energy into a train 220of electromagnetic energy, directing the train 220 of energy toward arectifier 214. The rectifier 214 directs the train 220 of energy towarda treatment zone 222 of the substrate support 202, or of a substratedisposed thereon. In one example, the apparatus 200 is configured toanneal a 2.2 m×2.6 m device within about 1 minute (e.g., 5.72 m²/min),or 60 substrates an hour.

The optical assembly 206 comprises a moveable reflector 208, which maybe a mirror, and an optical column 212 aligned with the reflector 208.The reflector 208 is mounted on a positioner 210 which, in theembodiment of FIG. 2, rotates to direct a reflected beam toward aselected location. In other embodiments, the reflector may translaterather than rotating, or may both translate and rotate. The opticalcolumn 212 forms and shapes pulses of energy from the energy sources204, reflected by the reflector 208, into a desired energy train 220 fortreating a substrate on the substrate support 202. An optical columnthat may be used as the optical column 212 for forming and shapingpulses is described in co-pending U.S. patent application Ser. No.11/888,433, filed Jul. 31, 2007, and published Feb. 5, 2009, as UnitedStates Patent Application Publication No. 2009/0032511, which is herebyincorporated by reference.

The rectifier 214 comprises a plurality of optical cells 216 fordirecting the energy train 220 toward the treatment zone 222. The energytrain 220 is incident on one portion of an optical cell 216, whichchanges the direction of propagation of the energy train 220 to adirection substantially perpendicular to the substrate support 202 andthe treatment zone 222. Provided a substrate disposed on the substratesupport 202 is flat, the energy train 220 leaves the rectifier 214travelling in a direction substantially perpendicular to the substrate,as well.

The optical cells 216 may be lenses, prisms, reflectors, or other meansfor changing the direction of propagating radiation. Successivetreatment zones 222 are treated by pulses of electromagnetic energy fromthe energy source 204 by moving the optical assembly 206 such that thereflector 208 directs the energy train 220 to successive optical cells216.

In one embodiment, the rectifier 214 may be a two-dimensional array ofoptical cells 216 extending over the substrate support 202. In such anembodiment, the optical assembly 206 may be actuated to direct theenergy train 220 to any treatment zone 222 of the substrate support 202by reflecting the energy train 220 toward the optical cell 216 above thedesired location. In another embodiment, the rectifier 214 may be a lineof optical cells 216 with dimension greater than or equal to a dimensionof the substrate support. A line of optical cells 216 may be positionedover a portion of a substrate, and the energy train 220 scanned acrossthe optical cells 216 to treat portions of the substrate located belowthe rectifier 214, multiple times if desired, and then the line ofoptical cells 216 may be moved to cover an adjacent row of treatmentzones, progressively treating an entire substrate by rows.

The energy source 204 of FIG. 2 shows four individual beam generatorsbecause in some embodiments, individual pulses in a pulse train mayoverlap. Multiple beam or pulse generators may be used to generatepulses that overlap. Pulses from a single pulse generator may also bemade to overlap by use of appropriate optics in some embodiments. Use ofone or more pulse generators will depend on the exact characteristics ofthe energy train needed for a given embodiment.

The interdependent function of the energy source 204, the opticalassembly 206 and the rectifier 214 may be governed by a controller 226.The controller may be coupled to the energy source 204 as a whole, or toindividual energy generators of the energy source 204, and may controlpower delivery to the energy source, or energy output from the energygenerators, or both. The controller 226 may also be coupled to anactuator (not shown) for moving the optical assembly 206, and anactuator (not shown) for moving the rectifier 214, if necessary.

FIG. 3A is a flow diagram summarizing a method 300 according to anotherembodiment. The method 300 of FIG. 3A is useful for forming verticallyintegrated monolithic crystalline semiconductor structures, such asthin-film solar cells. A similar method may be used to form anyvertically integrated monolithic crystalline semiconductor material,such as may be found in memory and photonic devices.

At 302, a photoconversion unit, which may be amorphous,microcrystalline, or polycrystalline, is formed on a substrate. Thephotoconversion unit may comprise a p-i-n junction formed from a dopedsemiconductor such as silicon, germanium, a CIGS semiconductor, or acombination thereof.

At 304, a p-type semiconductor layer is formed on the substrate bydepositing a semiconductor material using a vapor deposition process,such as physical or chemical vapor deposition, which may be plasmaenhanced, wherein the vapor comprises a semiconductor source and adopant source. The p-type semiconductor layer may be amorphous,microcrystalline, or polycrystalline.

At 306, the p-type layer is melted and recrystallized using laserpulses. A pulse train, or group of pulses, is formed by optically addinglaser pulses and homogenizing the resulting pulse train to form aspatially homogenized variable power electromagnetic energy beam. Thevariation in power, or energy per unit time, of each pulse train isdesigned to deliver electromagnetic energy to the p-type layer thatvaries to progressively melt the p-type layer. When the rate of energyincident on the p-type layer from a pulse or group of pulses, surpassesthe rate of heat diffusion through the p-type layer, and the localtemperature of the irradiated portion rises to a point greater than themelting point of the material, a molten area forms in the p-type layer.If the energy of the pulse(s) decreases, the rate of energy input nearthe interface between the solid phase and the melt phase may fall belowthe rate of heat diffusion from the melt phase into the solid phase, anda portion of the molten area may resolidify.

The precise details of the amplitude-time function of the energy beamgoverns the degree to which re-freezing occurs during local intensityminima, and may be used to select the mode of melting performed. Forexample, in one embodiment the energy beam may be designed to progressthe melt front by about 500 Å and re-freeze about 10 Å. In anotherembodiment, the melt front may be progressed by about 500 Å by eachlocal maximum, and each local minimum allows re-freezing of about 400 Å.Each successive energy maximum from one or more of the pulses may bedesigned to progress the melt front between about 60 Å and about 600 Ådeeper into the layer until the layer is substantially melted.

In the melt/recrystallize process, a plurality of treatment zones isdefined on the p-type layer, and each zone treated sequentially toconvert the p-type layer into a crystalline material. Each treatmentzone is treated after its immediate neighbor to provide a crystallineinterface at the edge of the treatment zone to stimulate crystal growthafter the melt operation. In one embodiment, each treatment zone isexposed to a plurality of overlapping pulses of electromagnetic energy,which may be formed into an energy modulated beam of radiation. Foruniform treatment of each treatment zone, the energy of the beam isuniformly distributed spatially across the zone, as described above.

In one embodiment, a portion of the p-type layer near the underlyinglayers may remain unmelted to minimize diffusion and/or mixing ofdopants of different types. For example, if the p-type layer is formedover an amorphous n-type layer in the underlying photoconversion unit,it may be desired to avoid melting up to about 100 Å of the p-type layerto avoid mixing or diffusion of p and n-type dopants at the interface.Even with use of a buffer layer between the p-type layer and theunderlying photoconversion unit, leaving a thin p-type buffer layerunmelted may be useful.

In one embodiment, it may be useful to form a thin layer of crystallinematerial between the photoconversion unit of operation 302 and thep-type layer of operation 304. A layer of crystalline material, such aspolycrystalline or monocrystalline silicon or other semiconductor, thatis less than about 50 Å thick and is used to help promote growth of acrystal structure in the p-type layer during freezing of the moltenmaterial. The layer of crystalline material may be continuous ordiscontinuous, and may be formed by deposition or by a localrecrystallization process. In a local recrystallization process, thecrystalline material may form a point or dot, a line, or a periodicsurface structure, for example by exposure to a spot beam ofelectromagnetic energy such as a laser.

Recrystallization of the p-type layer may be facilitated by modulatingthe energy beam by reducing the pulse frequency, pulse profile, or byusing longer wavelengths of light. Therefore, by reducing andcontrolling the rate of energy input maintains surface areas of thep-type layer in a molten state as recrystallization proceeds at thesolid-melt interface. Thus, a progressive recrystallization process maybe accomplished wherein crystallization proceeds from a location of themolten material near a subjacent layer to the surface of the moltenmaterial. Such a progressive recrystallization may enhance formation oflarge crystal grains by promoting ordered, directional crystalformation.

At 308, an i-type semiconductor layer, which may be amorphous,microcrystalline, or polycrystalline, is formed on the substrate using aprocess similar to that used to form the p-type layer, excluding thedopant source. The i-type layer is converted to a crystalline layer at310 by melting and recrystallizing in a process similar to that ofoperation 306. Finally, an n-type semiconductor layer is formed at 312and converted to crystalline form at 314 to complete the method.

The thickness of the layers formed in the method 300 may be up to about50 μm thick, as needed for the particular embodiment. In a solar cellembodiment, the layers will generally be less than about 2.5 μm thick,and may be as thin as about 100 Å to about 500 Å in some cases. Themelt/recrystallization process described above may be used to form apower generating region as the bulk of a solar cell, either as astand-alone crystalline solar cell or with a thin amorphous cell in atandem thin-film cell.

FIG. 3B is a schematic side-view of a substrate 350 formed according tothe method 300 of FIG. 3A. The substrate 350 comprises two powergenerating regions 358 and 366 between two conductive layers 374 and356, and protective layers 376 and 352, and a strength-enhancing layer354. Each of the power generating regions 358 and 366 comprises a p-typesemiconductor layer 372, 364, an i-type semiconductor layer 370, 362,and an n-type semiconductor layer 368, 360. The layers of the powergenerating regions 358 and 366 generally have different crystalmorphologies to facilitate the absorption of light across a widewavelength spectrum. In one embodiment, layers 360, 370 and 372 areamorphous, and layers 362, 364, and 368 are microcrystalline,polycrystalline, multicrystalline, or monocrystalline. The crystallinelayers may be formed by depositing amorphous layers and thenrecrystallizing each of the layers according to the method 300 of FIG.3A.

In one embodiment, the n-type semiconductor layer 360 is an amorphouslayer to provide oxygen barrier properties. In another embodiment, thep-type semiconductor layer 372 and the i-type semiconductor layer 370are each amorphous to collect shorter wavelength light. In an alternateembodiment, the n-type semiconductor layer 368 is amorphous, while then-type semiconductor layer 360 is crystalline to facilitate collecting abroad spectrum of light.

FIG. 4A is a plan view of a production system 490 for processingsubstrates according to another embodiment. The system 490 comprises acollection of substrate conveyors 450, 458, and processing stations 400,455, which may be used to form a thin-film photovoltaic device. In theembodiment of FIG. 4A, two groups of processing stations 400, each ofwhich may be a deposition station, are matched to two feed conveyors458, which collect substrates from the main conveyor 450 for processingand deposit processed substrates back on the main conveyor 450 fordelivery to the next processing stage. The embodiment of FIG. 4A isconfigured such that the processing stations 400 are deposition stationsand the processing stations 455 are thermal treatment stations, andafter processing in a processing station 400, a substrate is deliveredto a processing station 455 for thermal treatment. Each processingstation 455 may be a processing chamber for performing a crystallizationoperation as described above in connection with FIGS. 1A and 2. Each ofthe processing stations 400 may be used to form a p-i-n junction on asubstrate for a thin-film photovoltaic device, as described above inconnection with FIG. 3. Each processing station 400 comprises a transferchamber 470 coupled to a load lock chamber 460 and the process chambers481-487. The load lock chamber 460 allows substrates to be transferredbetween the ambient environment outside the system and vacuumenvironment within the transfer chamber 470 and process chambers481-487. The load lock chamber 460 includes one or more regions that maybe evacuated while enclosing one or more substrate. The load lockchamber 460 is pumped down when substrates enter from the ambientenvironment, and vented during delivery of substrates to the ambientenvironment from the processing station 400. The transfer chamber 470has at least one vacuum robot 472 disposed therein that is adapted totransfer substrates between the load lock chamber 460 and the processchambers 481-487. While seven process chambers are shown in processingstation 400 of FIG. 4A, each processing station 400 may have anysuitable number of process chambers.

In one embodiment of a processing station 400, one of the processchambers 481-487 is configured to deposit a p-type silicon layer(s) of afirst p-i-n junction 320 or a second p-i-n junction 330 of a solar celldevice, another one of the process chambers 481-487 is configured todeposit an intrinsic silicon layer of the first or the second p-i-njunction, and another of the process chambers 481-487 is configured todeposit the n-type silicon layer(s) of the first or the second p-i-njunction. While a process configuration having three types of chamberprocesses (i.e., a p-type process, an i-type process, and an n-typeprocess) may have some contamination control advantages, it willgenerally have a lower substrate throughput than a process configurationhaving two types of chamber processes (i.e., a p-type process and ani/n-type process), and is generally incapable of maintaining a desiredthroughput when one or more of the processing chambers are brought downfor maintenance.

FIG. 4B is a schematic cross-sectional view of one embodiment of aprocessing chamber, such as a PECVD chamber 401 in which one or morefilms of a solar cell may be deposited. In one embodiment, the chamber401 generally includes walls 402, a bottom 404, and a showerhead 410,and substrate support 430 which define a process volume 406. The processvolume is accessed through a valve 408 such that the substrate may betransferred in and out of the PECVD chamber 401. The substrate support430 includes a substrate receiving surface 432 for supporting asubstrate and stem 434 coupled to a lift system 436 to raise and lowerthe substrate support 430. A shadow frame 433 may be optionally placedover periphery of the device substrate 303 that may already have one ormore layers formed thereon, for example, the conductive layer 356. Liftpins 438 are moveably disposed through the substrate support 430 to movea substrate to and from the substrate receiving surface 432. Thesubstrate support 430 may also include heating and/or cooling elements439 to maintain the substrate support 430 at a desired temperature. Thesubstrate support 430 may also include grounding straps 431 to provideRF grounding at the periphery of the substrate support 430. Examples ofgrounding straps are disclosed in U.S. Pat. No. 6,024,044 issued on Feb.15, 2000 to Law et al. and U.S. patent application Ser. No. 11/613,934filed on Dec. 20, 2006 to Park et al.

The showerhead 410 is coupled to a backing plate 412 at its periphery bya suspension 414. The showerhead 410 may also be coupled to the backingplate by one or more center supports 416 to help prevent sag and/orcontrol the straightness/curvature of the showerhead 410. A gas source420 is coupled to the backing plate 412 to provide gas through thebacking plate 412 and through the plurality of holes 411 in theshowerhead 410 to the substrate receiving surface 432. A vacuum pump 409is coupled to the PECVD chamber 401 to control the process volume 406 ata desired pressure. An RF power source 422 is coupled to the backingplate 412 and/or to the showerhead 410 to provide a RF power to theshowerhead 410 so that an electric field is created between theshowerhead and the substrate support so that a plasma may be generatedfrom the gases between the showerhead 410 and the substrate support 430.Various RF frequencies may be used, such as a frequency between about0.3 MHz and about 200 MHz. In one embodiment the RF power source isprovided at a frequency of 13.56 MHz. Examples of showerheads aredisclosed in U.S. Pat. No. 6,477,980 issued on Nov. 12, 2002 to White etal., U.S. Publication 2005/0251990 published on Nov. 17, 2006 to Choi etal., and U.S. Publication 2006/0060138 published on Mar. 23, 2006 toKeller et al, which are all incorporated by reference in their entiretyto the extent not inconsistent with the present disclosure.

A remote plasma source 424, such as an inductively coupled remote plasmasource, may also be coupled between the gas source and the backingplate. Between processing substrates, a cleaning gas may be provided tothe remote plasma source 424 so that a remote plasma is generated andprovided to clean chamber components. The cleaning gas may be furtherexcited by the RF power source 422 provided to the showerhead. Suitablecleaning gases include but are not limited to NF₃, F₂, and SF₆. Examplesof remote plasma sources are disclosed in U.S. Pat. No. 5,788,778 issuedAug. 4, 1998 to Shang et al, which is incorporated by reference to theextent not inconsistent with the present disclosure.

FIG. 5A is a process flow diagram summarizing a method 500 according toanother embodiment. The method 500 is useful for forming a crystallinephotovoltaic device 550. FIG. 5B is a schematic cross-sectional view ofpart of a crystalline photovoltaic device 550, having a crystallinesubstrate 551 and doped layer 552. At 502, a substrate is provided forconstructing the photovoltaic device. The substrate will generally havea contact portion 553 disposed on a surface of the crystalline substrate551. The contact portion 553 is conductive, and generally formed from ametal. The crystalline substrate 551 will generally be a semiconductormaterial such as silicon, silicon-germanium, CIGS, or a group III/Vcompound semiconductor. A doped silicon substrate may be monocrystalline(e.g., Si<100> or Si<111>), microcrystalline, multicrystalline,polycrystalline, strained, or amorphous.

The doped layer 552 is generally a semiconductor layer doped with ap-type or n-type dopant to create electron surplus or deficiency. Thesemiconductor material may be any semiconductor generally used formaking crystalline solar cells, such as silicon, germanium,silicon-germanium alloy, CIGS, or group III/V compound semiconductors,and may be formed by any convenient process, such as physical orchemical vapor deposition, with or without plasma enhancement. In ann-type layer, donor type atoms are doped within the crystallinesemiconductor substrate during the substrate formation process. Suitableexamples of donor atoms include, but not limited to, phosphorus (P),arsenic (As), antimony (Sb). In a p-type layer, acceptor type atoms,such as boron (B) or aluminum (Al), may be doped into the crystallinesilicon substrate during the substrate formation process. The substrateis typically between about 100 μm and about 400 μm thick.

At 504, a doped semiconductor layer 552 is formed on the substrate. Thedopant type of the doped semiconductor layer is generally opposite thatof the doped layer on the substrate. Thus, if the substrate 551 featuresa p-type doped layer, an n-type layer is formed, and vice versa. Thep-type and n-type layers form a p-n junction region near the interfacebetween the two layers. The semiconductor material used for the dopedsemiconductor layer may be the same as the semiconductor layer of thesubstrate, or different. In one embodiment, the doped layer of thesubstrate and the doped semiconductor layer formed thereon are bothdoped silicon layers. The doped semiconductor layer may be formed by anyconvenient process, such as physical or chemical vapor deposition, withor without plasma enhancement. In one embodiment, the dopedsemiconductor layer is formed by a plasma-enhanced chemical vapordeposition process in an apparatus similar to that described in FIG. 4B.The doped semiconductor layer will generally be less than about 50 μmthick, and in many embodiments will be about 2 μm thick or less, and maybe amorphous, microcrystalline, or polycrystalline.

At 506, the doped semiconductor layer is crystallized using a thermalprocess similar to that described in connection with FIG. 1A above,using a treatment device that is similar to apparatus 200 discussedabove. In one embodiment, a plurality of treatment zones is defined onthe doped semiconductor layer, and each treatment zone is exposed topulsed electromagnetic energy to progressively melt the treatment zoneand then crystallize the melted portion. The pulses may be laser ormicrowave pulses, and are generally homogenized to produce uniformradiant spatial intensity across the treatment zone. The instantaneousintensity, profile and duration of each pulse is defined to move a meltfront partway through the doped semiconductor layer. For example, asdescribed above, each pulse may move the melt front between about 60 Åand about 600 Å deeper into the doped semiconductor layer. As alsodescribed above, the pulses may overlap or be separated by a restduration.

The number of pulses delivered is selected to reach an end point, whichmay be the interface between the doped semiconductor layer and theunderlying layer, or some proximity to that interface. After reachingthe end point, the melted region is allowed to crystallize, using theunderlying crystal structure, and the crystal structure of a neighboringcrystallized treatment zone, as seed material. The treatment zones areprocessed sequentially by moving the electromagnetic energy, or thesubstrate, or both, so that each treatment zone is processed followingits immediate neighbor.

At 508, typically patterned electrical contacts 555 are formed on thesurface 556 of the treated layer 552 disposed over the substrate 551 tocomplete the photovoltaic cell. An anti-reflective layer 554 may also beformed over the surface 556 to reduce light reflection at the surface ofthe device. In this way, a crystalline photovoltaic device may be formedwithout relying on comparatively slow processes to deposit crystallinelayers from a vapor phase.

In some embodiments, the melt end point may be defined some distancefrom the interface to avoid intermingling of p-type and n-type dopants.In embodiments featuring a p-type layer in close proximity, or even incontact with, an n-type layer, the melt end point may be defined about20 Å or less from the interface between the layers. A thin unmeltedlayer is left between the crystalline layers as a buffer to preventdopant intermingling. In one embodiment, the buffer layer may also becrystallized by directing sub-melt pulses through the melt phase intothe buffer layer. If delivered before the melt phase beginscrystallizing, a plurality of electromagnetic energy pulses may bedirected toward the surface of the melt phase, and may propagate throughthe melt phase to the buffer layer, each pulse delivering enough energyto the buffer layer to cause incremental reorganization of the atomicstructure of the buffer layer into a crystalline structure withoutmelting the buffer layer and without causing significant dopantmigration.

In one embodiment, a treatment program may be delivered to asemiconductor layer, which may be amorphous, microcrystalline, orpolycrystalline, to melt and crystallize the layer without significantmigration of atoms between the treated layer and an underlyingcrystalline layer found in the substrate. A first group of one or morepulses of electromagnetic radiation is delivered to the surface 556 ofthe doped semiconductor layer 552 to begin the melt process. Each pulseof the first group will have energy enough to melt a portion of thesurface, and may have the same energy content as the other pulses of thefirst group, or may have a different energy content. The first group ofpulses forms a melt phase, with a melt front at the interface betweenthe melt phase and the solid phase.

A second group of one or more pulses is delivered to the semiconductorlayer to progress the melt front through the semiconductor layer to anend point. Each pulse of the second group has energy content sufficientto propagate through the melt phase and deliver enough energy to thesolid phase to melt a portion of the solid phase, thus progressing themelt front. The power delivered by the second group of pulses isgenerally higher than that delivered by the first group of pulses. Toavoid migration of atoms between the semiconductor layer and anunderlying crystalline layer, the melt end point is defined a shortdistance from the interface between the semiconductor layer and theunderlying crystalline layer. The region between the melt end point andthe interface may be a buffer layer.

After the second group of pulses is delivered, the melt front reachesthe end point, and a third group of one or more pulses is delivered tothe semiconductor layer to crystallize the buffer layer without melting.Each pulse of the third group has energy content enough to propagatethrough the melt phase and deliver energy to the buffer layer sufficientto incrementally crystallize the atoms in the buffer layer withoutmelting and without substantial migration of atoms between thesemiconductor layer and the underlying crystalline layer. After deliveryof the third group of pulses, the melt phase is crystallized, thecrystal structure of the melt phase developing from the crystalstructure of the buffer layer and the underlying crystalline layer.

As described above, the first and second group of pulses may overlap, ormay be separated by a rest duration, the degree of overlap or separationselected to allow partial refreezing of the melt phase before the nextpulse of energy arrives. The third group of pulses may likewise overlapor be separated, but because the third group of pulses is designed toavoid melting, the duration, intensity, and frequency of the third groupof pulses will generally be selected to allow the buffer layer to returnto an ambient energy state after each pulse before the next pulsearrives. Thus, the third group of pulses may deliver a power level lessthan the second group of pulses, and may be less than the power level ofthe first group of pulses.

FIG. 6 schematically illustrates pulses of energy according to anotherembodiment. In one embodiment, multiple energy pulses having differingintensities may be useful in crystallizing a semiconductor layer formedover a crystalline layer using a melt/recrystallization process whileminimizing migration of atoms between the two layers. In one example,pulses 601, 602, and 603 that have respective intensities I₁, I₂, and I₃are delivered to the semiconductor layer. In one example, as shown inFIG. 6, one or more of the pulses, such as pulses 602 ₁ through 602 _(N)and 603 ₁ through 603 _(N) may comprise a group of pulses. In oneembodiment, the intensity of the first pulse type 601 is lower than theintensity I₂ of the second pulse type 602. As described above, the firstpulse type 601 impacts the semiconductor layer and liquefies a portionthereof. The second pulse type 602 impacts the liquid surface of thesemiconductor, propagates through the liquid phase, and impacts theunderlying solid phase, melting a portion of the underlying solid phaseand progressing a melt front through the semiconductor layer to an endpoint. The third pulse type 603, has intensity I₃ lower than those ofpulse types 601 and 602, and propagates through the liquid phase todeliver energy to the buffer layer that incrementally recrystallizes thebuffer layer without melting, thus minimizing the opportunity formigration of atoms from the buffer layer to the underlying crystallinesemiconductor layer. In the embodiment of FIG. 6, the N pulses of thesecond pulse type are shown overlapping in time. The M pulses of thethird pulse type 603 may overlap in time, or may be separated by periodsof ambient energy.

In one embodiment, an amorphous silicon layer of thickness 1.5 μm, incontact with an underlying crystalline layer, is crystallized using apulsed laser treatment. The amorphous silicon layer is divided intotreatment zones, and each treatment zone is subjected to a series ofpulses from a 1064 nm laser, the series of pulses comprising one pulseof duration 10 ns delivering 0.35 J/cm², followed by 10 pulses, each of10 ns duration, each delivering 0.5 J/cm², and each overlapping withpulses on either side by 25%, followed by 5 pulses, each of 10 nsduration, each delivering 0.3 J/cm², and each separated by a restduration of 10 ns. The pulsed laser treatment described above willcrystallize the amorphous silicon layer while minimizing migration ofatoms between the two layers.

In another aspect, other types of devices may benefit from a rapidcrystalline semiconductor formation process such as that describedherein. FIG. 7 is a schematic cross-sectional view of a device 700according to an embodiment. The device 700 generally comprises acrystalline semiconductor layer 704, which may have a polycrystalline ormonocrystalline morphology, between two functional layers 702 and 706.The functional layers 702 and 706 may each be a metal layer, for examplean electrode, a dielectric layer, such as a metal oxide layer, or asemiconductor layer.

In one embodiment, the device 700 may be a memory device, wherein thefunctional layers 702 and 706 are metal layers and the crystallinesemiconductor layer 704 is a memory cell. The memory cell may be formedin a method similar to that used to form the semiconductor layers of thephotovoltaic devices described above. A semiconductor layer is formed byphysical or chemical vapor deposition, and crystallized according to themelt/recrystallization processes described above in connection withFIGS. 1A, 3A, and 5A. The semiconductor layer may be doped with p-typedopants such as boron, aluminum, gallium, and indium, and n-type dopantssuch as phosphorus and arsenic, which may be used to form a p-n or p-i-njunction. The semiconductor material may be any elemental or compoundsemiconductor material suitable for memory applications, such a group IVsemiconductor, a group III/V (group 13/15) semiconductor, or a groupII/VI (group 12/16) semiconductor. Some exemplary semiconductorsinclude, but are not limited to silicon, germanium, silicon-germanium,CIGS materials, nitrides or phosphides of gallium, aluminum, and indium,sulfides, selenides, or tellurides or zinc, cadmium, and mercury, and soon. A crystalline seed layer may be deposited before forming theamorphous semiconductor layer to aid the recrystallization process. Thecrystalline seed layer may be formed by any process suitable for formingcrystalline layers, such as a vapor phase epitaxy or chemical vapordeposition.

A plurality of discrete charge storage particles may be embedded in thecrystallized layer in some embodiments. The discrete charge storageparticles may improve the density of charge that can be fixed in thememory cell. The discrete charge storage particles, which may be metalatoms or atom clusters, may be deposited by any suitable depositionprocess, such as PVD or CVD, between two crystalline layers, or may beimplanted by ion beam or plasma immersion ion implantation. In adeposition process, a first semiconductor layer is formed on asubstrate, the discrete charge storage particles are deposited on thefirst semiconductor layer, and a second semiconductor layer is formed onthe discrete charge storage particle layer. The first and secondsemiconductor layers may each be, individually, amorphous,microcrystalline, or polycrystalline. The entire structure is thenrecrystallized by a pulsed energy melt process, as described above.

In another embodiment the device 700 may be a photonic device, such as alight-emitting diode (LED). In an LED embodiment, the functional layer702 is generally a dielectric substrate, such as sapphire, that providesstructural support for the active portions of the device. The functionallayer 702 may also include a buffer layer or transition layer formed onthe surface of the functional layer 702 to facilitate compatibilitybetween the functional layer 702 and the crystalline semiconductor layer704 to be formed thereon. The crystalline semiconductor layer 704 isgenerally a group III nitride semiconductor such as gallium nitride,aluminum nitride, indium nitride, or mixtures thereof. The surface ofthe functional layer 702 may thus be treated to form a thin layer ofaluminum nitride or a mixture of nitrides of aluminum, gallium, andindium, as a buffer layer or transition layer.

The crystalline semiconductor layer 704 in the LED embodiment isgenerally a group III nitride layer, and may comprise gallium nitride,aluminum nitride, and indium nitride. The crystalline semiconductorlayer 704 comprises a multi-quantum well material, such as indiumgallium nitride, as an active component. The crystalline semiconductorlayer 704 also generally comprises an undoped nitride layer, such asgallium nitride, and an n-type doped nitride layer, which may also begallium nitride doped with an n-type dopant such as those describedabove.

The functional layer 706 in the LED embodiment is generally a p-typedoped group III nitride layer, such as a gallium nitride or aluminumgallium nitride layer doped with a p-type dopant.

The layers in the LED device are generally formed by a chemical vapordeposition process, and/or hydride vapor phase epitaxy (HVPE) process,in which a group III metal such as gallium, indium, or aluminum, isexposed to a halogen source such as hydrogen chloride to form a groupIII metal halide, which in turn is mixed with a nitrogen source such asammonia to form the group III nitride material, as is known in the art.The layers deposited by such a process may be crystallized into apolycrystalline or monocrystalline morphology using the pulsed energymelt crystallization process described above in connection with FIGS.1A, 3A, and 5A.

It should be noted that in all instances of forming a multi-layersemiconductor device, all semiconductor layers in the device may becrystallized using the pulsed energy melt crystallization processesdescribed herein, or only selected layers may be crystallized. In oneembodiment, all semiconductor layers in the device may be formed havingamorphous, microcrystalline, or polycrystalline morphology, and then alllayers are recrystallized using a single progressive pulsed energymelt/recrystallization process. In another embodiment, individual layersselected to be crystallized may be subjected to a pulsed energymelt/recrystallization process before forming a subsequent layer. It isbelieved that the process of crystallizing, or recrystallizing, onelayer at a time can be effectively used to individually process eachlayer without significantly affecting the crystalline structure orcomposition of adjacent layers, due to the controlled delivery and shortduration of the energy delivered during the pulsed energy meltcrystallization process. Using such methods, devices havinghigh-efficiency crystalline semiconductor components withpolycrystalline or monocrystalline morphology may be manufactured in acost-efficient, high-throughput process.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

What is claimed is:
 1. A method of treating a substrate, comprising:identifying a first treatment zone; forming a molten area of the firsttreatment zone by exposing a surface of the first treatment zone to afirst laser pulse, wherein the first laser pulse has a non-uniformity ofless than about 5 percent; recrystallizing the molten area of the firsttreatment zone while exposing the first treatment zone to a plurality oflaser pulses; identifying a second treatment zone; and repeating theforming a molten area and the recrystallizing the molten area with thesecond treatment zone.
 2. The method of claim 1, wherein the forming amolten area of each treatment zone further comprises exposing thesurface of each treatment zone to a second laser pulse, and a durationbetween the first laser pulse and the second laser pulse is less than atime necessary for a portion of the molten area to refreeze.
 3. Themethod of claim 2, wherein the first laser pulse and the second laserpulse have the same duration and intensity.
 4. The method of claim 1,wherein each pulse of the plurality of laser pulses has the sameduration and intensity as the first laser pulse.
 5. The method of claim1, wherein each pulse of the plurality of laser pulses has a duration oran intensity that is different from the first laser pulse.
 6. The methodof claim 1, wherein the second treatment zone and the first treatmentzone share a boundary.
 7. The method of claim 5, wherein the forming amolten area of each treatment zone further comprises exposing thesurface of each treatment zone to a second laser pulse, and a durationbetween the first laser pulse and the second laser pulse is less than atime necessary for a portion of the molten area to refreeze.
 8. Themethod of claim 1, wherein a duration between each pulse of the secondplurality of laser pulses is more than a time to freeze the portion ofthe first treatment zone.
 9. The method of claim 1, wherein each pulseof the plurality of laser pulses melts a portion of a recrystallizedarea.
 10. The method of claim 1, wherein the second treatment zone isadjacent to the first treatment zone.
 11. The method of claim 1, whereineach pulse of the plurality of laser pulses melts a portion of arecrystallized area and the second treatment zone is adjacent to thefirst treatment zone.
 12. A method of treating a substrate, comprising:identifying a first treatment zone; forming a molten area of the firsttreatment zone by exposing a surface of the first treatment zone to afirst group of one or more laser pulses and a second group of one ormore laser pulses; recrystallizing the molten area of the firsttreatment zone while exposing the first treatment zone to a third groupof one or more laser pulses, wherein a power delivered by the thirdgroup of one or more laser pulses is less than a power delivered by thefirst group of one or more laser pulses and a power delivered by thesecond group of one or more laser pulses; identifying a second treatmentzone adjacent to the first treatment zone; and repeating the forming amolten area and the recrystallizing the molten area with the secondtreatment zone.
 13. The method of claim 12, wherein first one or morelaser pulses are separated from the second one or more laser pulses by arest duration, wherein the rest duration allows partial refreezing ofthe molten area before a subsequent pulse arrives.
 14. The method ofclaim 12, wherein the first group of one or more pulses is one pulse,the second group of one or more pulses comprises multiple pulses and thethird group of one or more pulses comprises multiple pulses.
 15. Themethod of claim 14, wherein the multiple pulses of the second group ofone or more pulses overlap in time.
 16. The method of claim 15, whereinthe multiple pulses of the third group of one or more pulses areseparated by a rest duration.
 17. A method of treating a substrate,comprising: identifying a first treatment zone; forming a molten area ofthe first treatment zone by exposing a surface of the first treatmentzone to a first plurality of laser pulses; recrystallizing the moltenarea of the first treatment zone while exposing the first treatment zoneto a second plurality of laser pulses, wherein each pulse of the secondplurality of laser pulses melts a portion of a recrystallized area;identifying a second treatment zone adjacent to the first treatmentzone; and repeating the forming a molten area and the recrystallizingthe molten area with the second treatment zone.
 18. The method of claim17, wherein each pulse of the first plurality of laser pulses has aduration between about 1 ns and about 50 ns.
 19. The method of claim 18,wherein each pulse of the first plurality of laser pulses has a durationbetween about 20 ns and about 30 ns.
 20. The method of claim 17, whereineach pulse of the first plurality of laser pulses delivers a powerbetween about 10⁷ W/cm² and about 10⁹ W/cm².